Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $91.97   3.604%   $95.2846   $95.28   $95.30   $95.30  
  Purchase #2 $151.49   7.604%   $163.0093   $163.01   $163.00   $163.00  
  Purchase #3 $96.44   13.312%   $109.2781   $109.28   $109.30   $109.30  
  Purchase #4 $219.31   6.348%   $233.2318   $233.23   $233.25   $233.20  
  Purchase #5 $237.75   7.119%   $254.6754   $254.68   $254.70   $254.70  
  Purchase #6 $104.41   11.608%   $116.5299   $116.53   $116.55   $116.50  
  Purchase #7 $47.51   13.603%   $53.9728   $53.97   $53.95   $54.00  
  7 purchase totals = $948.88       $1,025.9819   $1,025.98   $1,026.05   $1,026.00